1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a semiconductor substrate, and more particularly to a method and apparatus for efficiently manufacturing a silicon substrate on which an epitaxial layer is grown.
2. Description of the Related Art
A conventional example of a method of manufacturing a silicon substrate on which an epitaxial layer is grown will be described below with reference FIG. 1A to 1G.
In the conventional example of the manufacturing method, as shown in FIG. 1A, a silicon single crystal ingot 11 is cut out and then a rounding process is performed. In the slicing process which is shown in FIG. 1B, a silicon substrate 12 having a wafer shape is cut down from the silicon single crystal ingot 11 which is subjected to a cutting process and a rounding process.
Next, as shown in FIG. 1C, a beveling process is performed to cut down corners in the peripheral portion of the silicon substrate 12. Subsequently, as shown in FIG. 1D, a mechanical polishing (lapping) process is performed to make the surface of the silicon substrate 12 even, so that flaws on the surface are made small and the parallel degree is increased.
Next, as shown in FIG. 1E, a damage layer which has been formed in the surface layer of the silicon substrate 12 during the mechanical polishing process is removed by etching. Thereafter, a blocking film forming process is performed to form a blocking film 13 on the front and rear surfaces 12F and 12B of the silicon substrate 12 so as to prevent an auto-doping phenomenon.
Subsequently, as shown in FIG. 1F, a mirror polishing process is performed. In the mirror polishing process, flaws on the substrate surface which can not be removed in the mechanical polishing process is removed by a chemical mechanical polishing (CMP) method such that the surface of the silicon substrate 12 is made shaped like a mirror.
Finally, as shown in FIG. 1G, an epitaxial silicon layer 14 is formed on the surface of polished silicon substrate 12.
In this way, a semiconductor substrate (a wafer) 15 on which the epitaxial silicon layer 14 has been grown on the silicon substrate 12 is manufactured.
Generally, the silicon substrate 12 is often formed to have a high density of impurity ions doped into either of a P type or N type conductive type. Also, in order to perform the epitaxial growth on the silicon substrate 12, the silicon substrate 12 must be heated to a temperature in a range of 1000 to 1200.degree. C. The impurity ions such as boron ions, phosphorus ions, antimony ions and arsenic ions are doped in the silicon substrate 12. Therefore, when the silicon substrate having a high density of impurity ions doped is heated in the stage in which the blocking film 13 is not formed, the impurity ions doped in the silicon substrate 12 escape from the silicon substrate 12 due to the heat. As a result, the so-called auto-doping phenomenon occurs, that is, the impurity ions enter into the epitaxial growth layer 14. This phenomenon changes the electric characteristic of the silicon substrate with the epitaxial growth layer 14. Therefore, in the manufacturing process of the silicon substrate with the epitaxial growth layer, it is absolutely necessary to form the blocking film 13. The blocking film 13 is generally formed of a silicon oxide film (SiO.sub.2), a silicon nitride film (Si.sub.3 N.sub.4) or the like, using a CVD method, a thermal oxidation method, a thermal nitride method and so on.
In the conventional technique which is shown in FIGS. 1A to 1G, the blocking film 13 is formed on a front surface 12F of the silicon substrate on which the epitaxial layer 14 is formed where semiconductor elements are formed, and a rear surface 12B opposite to the front surface 12F. The blocking film 13 on the front surface 12F is removed in the chemical mechanical polishing process such that the front surface 12F is exposed, as shown in FIG. 1F.
However, when the blocking film 13 is removed through the mirror polishing process in this way, there is the possibility that new flaws are formed on the surface in the removal of the blocking film. In accordance with, in order to remove the new flaws and to achieve the mirror surface of the silicon substrate, the mirror polishing process needs to be performed for a long time.
Also, the technique that the mirror polishing process is performed to both surfaces of the silicon substrate for improvement of the parallel degree and for reduction of the number of processes can not be applied to the manufacturing method shown in FIGS. 1A to 1G. This is because the blocking film as the essential film is removed from the both surfaces.
Further, in the manufacturing method shown in FIGS. 1A to 1G, when the mirror polishing process is performed to the both surfaces before the blocking film is formed, productivity decreases. This is because the two chemical mechanical polishing processes, i.e., the mirror polishing process for polishing the both surfaces and the mirror polishing process for removing the blocking film become necessary.